1. Field of the Invention
The present invention relates generally to integrated circuits. More specifically, but without limitation thereto, the present invention relates to packaging of integrated circuits for high-reliability, including, for example, shielding of the integrated circuits from radiation, such as ionizing radiation.
2. Discussion of the Background Art
Various applications in which integrated circuit devices are employed place demands on the integrated circuit devices not typically present in consumer applications. For example, in space satellite applications, ionizing radiation is present in the space environment at levels that often results in an integrated circuit die being exposed to an amount of radiation in excess of the integrated circuit die's total dose tolerance. As a result, the integrated circuit die can become damaged, or perform improperly, such as drifts in parametric performance or loss of functionality. Thus, the integrated circuit device may become unreliable.
Furthermore, excess heat buildup within the integrated circuit device can result in the integrated circuit die operating at a tempers cure in excess of its temperature operating range, in turn potentially resulting in damage to the integrated circuit die, or unreliable performance of the integrated circuit due, such as by the generation of errors
At the same time, integrated circuit devices that are sent into space must be robust enough to survive the launch of a spacecraft from earth, deployment in space, and potentially some amount of impact-related trauma once deployed. As a result, not only must an integrated circuit device used in space provide or be used in conjunction with a mechanism for preventing the exposure of the integrated circuit die to ionizing radiation in excess of its total dose tolerance, and provide or be used in conjunction with a mechanism for maintaining the temperature of the integrated circuit die within its temperature operating range, while at the same time maintaining or increasing the mechanical robustness of the integrated circuit package.
Another important aspect of integrated circuit devices that are sent into space is that such integrated circuit devices must be light weight enough to meet weight constraints inherent in integrated circuit devices that are launched from earth to space, e.g., earth orbit. Thus, in addressing the need for a mechanism for preventing the exposure of the integrated circuit due to ionizing radiation in excess of its total dose tolerance and the need for a mechanism for maintaining the temperature of the integrated circuit due within its operating range, and the requirement for mechanical robustness, the integrated circuit device for use in a space environment must be light weight.
Accordingly, in many radiation environments integrated circuit die must be shielded from radiation in order to function reliably. For example, as mentioned above, in a space environment, integrated circuit die must be, for example, shielded from ionizing radiation or the circuit may fail to function reliably. Additionally, the integrated circuit die may need to be shielded from, e.g., x-rays that can damage the circuit die, thus, causing it to fail or function unreliably. In a space environment, servicing, e.g., replacing a part that has failed or otherwise become unreliable is extremely expensive or all-together impossible. Thus, an integrated circuit die to be used in a space environment should shielded from one or both of ionizing radiation and x-ray radiation in order to function reliably.
Always, when packaging integrated circuit die for use in a high radiation environment such as space, the size and weight of the package is a major concern both due to weight limitations inherent in a space launch and relationship between weight and inertial mechanical forces to which the electronic circuit device will be subjected. Thus, an integrated circuit device that is very bulky or heavy adds not only cost to the launch of the systems in which the integrated circuit device is used, but, perhaps more importantly, reduces the reliability of the integrated circuit device. For example, the integrated circuit device may become unreliable because the weight of the part results in more stress on solder joints within the integrated circuit device, such as solder joints that connect the integrated circuit device to the circuit board, or solder joints that affix the lid of the integrated circuit device package. Thus, a reduction in the weight of an integrated circuit device benefits the integrated circuit device not only in making it lighter, and thus reducing the weight of the system, but results in less stress on the solder joints, and thus increases the reliability of the integrated circuit device, and the system in which the integrated circuit device is employed.
Heretofore, multi-chip modules provided integrated circuit devices comprising a package, and multiple integrated circuit die within a single-layered integrated circuit device package. The multi-chip module needs enough shielding material, either in its package, externally, or both, to shield the most sensitive of the multiple integrated circuit die within the multi-chip module, in order to assure the reliability of the most sensitive integrated circuit die within the multi-chip module. The amount of shielding material necessary to effect this amount of shielding, results not only in an unacceptably high weight, but an unacceptably high cost, as elaborated upon below.
Additionally, the amount of external shielding material in a multi-chip module (or a single-chip integrated circuit device), particularly when the integrated circuit device is designed for sensitive integrated circuit die and/or harsh space environments, greatly reduces the consistency with which a hermetic seal between the lid of the integrated circuit package and the sidewalls or base of the integrated circuit package. As the amount, e.g., thickness, of the shielding material required becomes greater, the ability of manufacturing processes to achieve a hermetic seal between the lid and the sidewalls or base is becomes less. This is because the shielding material, in additional to providing shielding of the integrated circuit dice within the multi-chip module (or single-chip integrated circuit device), acts as a heat sink, thus affecting the soldering process used to achieve a hermetic seal between the lid and the sidewalls or base. A hermetic seal between the lid and sidewalls or base is important, however, as such hermetic seal keeps moisture and other chemical contaminants from infiltrating the integrated circuit device, and causing deterioration of the integrated circuit dice, thus causing failure of the integrated circuit device or a reduction in the reliability of the integrated circuit device.
The ability to obtain a hermetic seal also decreases as the size of the integrated circuit device package increases. Both the shielding material, such as may be used in the lid, and the material used for the sidewalls and/or base of the integrated circuit device package expand and contract in response to thermal variations at certain rates depending upon the materials employed. As the length of the seal between the lid and the sidewalls or base increases, the amount of the difference between the amounts of the expansion or contraction in response to thermal variations of the lid verses the sidewalls or base increases. This results in warping at the interface between the lid and the sidewalls or base, which, in turn, decreases the ability of manufacturing processes to obtain a hermetic seal because the stress and strain at such interfaces increases. As described above, this inability to achieve a lack of hermeticity is undesirable.
As will be readily appreciated by one of ordinary skill in the art, the problems described above, while attributed to integrated circuit devices designed for use in space environments, are present in other environments as well. Thus, the embodiments described below will be appreciated as having numerous applications beyond space applications. For example, thermal (heat) dissipation is a significant issue in high-volume, high-density devices. The embodiments described herein provide a significant improvement to heretofore known devices with respect to thermal dissipation.
Specifically, as the need for large amounts of memory, and other high-volume integrated circuit devices, has increased with the increase in complexity, processing capacity and processor bits, the need for compact memory storage devices, and other high-volume and high-density integrated circuit devices, has increased. Large amounts of circuitry, such as high-volume memory modules, produce large amounts of heat that can ultimately cause the high-volume memory modules to fail or otherwise become unreliable. Prior approaches to packaging high-volume, high-density memory modules involve stacking multiple memory chips in plastic packages on top of one another. Traditional plastic packaging of the memory chips does not provide enough heat dissipation for a high-reliability high-volume, high-density memory module. The lack of an ability to adequately dissipate heat leads to larger integrated circuit devices and less circuit density. Furthermore, the lack of ability to dissipate heat, leads to increased integrated circuit device failure or unreliability.
Thus there is a need for improved integrated circuit devices and methods to address the numerous problems articulated above, as well as others.